Kavli Affiliate: Luis C. Ho
| First 5 Authors: Boris S. Kalita, Si-Yue Yu, John D. Silverman, Emanuele Daddi, Luis C. Ho
| Summary:
Recent JWST observations have revealed the prevalence of spiral structures at
$z > 1$. Unlike in the local Universe, the origin and the consequence of
spirals at this epoch remain unexplored. We use public JWST/NIRCam data from
the COSMOS-Web survey to map spiral structures in eight massive ($>
10^{10.5},rm M_{odot}$) star-forming galaxies at $z_{rm spec} sim 1.5$. We
present a method for systematically quantifying spiral arms at $z>1$, enabling
direct measurements of flux distributions. Using rest-frame near-IR images, we
construct morphological models accurately tracing spiral arms. We detect
offsets ($sim 0.2 – 0.8,rm kpc$) between the rest-frame optical and near-IR
flux distributions across most arms. Drawing parallels to the local Universe,
we conclude that these offsets reflect the presence of density waves. For nine
out of eighteen arms, the offsets indicate spiral shocks triggered by density
waves. Five arms have offsets in the opposite direction and are likely
associated with tidal interactions. For the remaining cases with no detected
offsets, we suggest that stochastic ‘clumpy’ star formation is the primary
driver of their formation. In conclusion, we find a multi-faceted nature of
spiral arms at $z > 1$, similar to that in the local Universe.
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